As a type of mounting device which is interposed between members constituting a vibration transmitting system for connecting these members in a vibration damping/isolating manner, such as an engine mount or differential gear mount for automobiles, a so-called fluid-filled mounting device is known as disclosed in laid-open Publication No. 55-107142 of unexamined Japanese Patent Application. In the fluid-filled mounting device, a pressure-receiving chamber and an equilibrium chamber are provided between a first support metal member and a second support metal member which are connected integrally with each other by an elastic rubber body, such that the pressure-receiving and equilibrium chambers, are held in communication with each other via an orifice passage. The mounting device is capable of exhibiting an excellent vibration-damping effect, due to a resonance of the fluid within the orifice passage based on relative pressure changes which occur between the pressure-receiving chamber and the equilibrium chamber upon application of vibrations. Such an effect cannot be obtained by a mounting device having an elastic body alone.
When the fluid-filled mounting device as described above receives the vibrations in a frequency range which is higher than the resonance frequency of the fluid flowing through the orifice passage, the resistance to the flows of the fluid through the orifice passage is extremely increased. For example, the above-described mounting device is employed as an engine mount used for automobiles. In this case, if the resonance frequency of the fluid flowing through the orifice passage is set within a low frequency range so a to obtain improved vibration-damping characteristics against the input vibrations in the low frequency range, such as engine shakes, the dynamic spring constant of the mount is unavoidably increased when the mount receives vibrations in a high-frequency range. Thus, the engine mount suffers from considerably poor isolating capability with respect to high frequency vibrations, such as engine idling vibrations and booming noises.
There has been proposed in laid-open Publication No. 57-9340 of unexamined Japanese Patent Application and others, a so-called fluid pressure absorbing mechanism having a movable plate which is disposed between the pressure-receiving chamber and the equilibrium chamber such that the movable plate is displaceable or deformable by a predetermined distance. This mechanism is adapted to absorb a pressure change within the pressure-receiving chamber upon application of the vibrations in a high frequency range. The fluid pressure absorbing mechanism as described above, however, can exhibit a sufficient pressure absorption effect with respect to only the input vibrations having a frequency up to 200 Hz, since the surface area of the movable plate is limited, for example. Thus, it was difficult to obtain sufficient isolating capability with respect to the input vibrations in a high frequency range.
Further, laid-open Publication No. 60-249749 of unexamined Japanese Patent Application discloses another mounting device having a plate-like oscillating member which is disposed within the pressure-receiving chamber while being supported by the first or second support metal member so as to extend in a direction perpendicular to the load-receiving direction, so that an annular flow restricting passage is formed between the oscillating plate and an inner wall of the pressure-receiving chamber. Such a mounting device can provide a low dynamic spring constant when the input vibrations in a high frequency range are applied thereto, due to a resonance of the fluid flowing through the restricting passage. In the mounting device constructed as described above, however, when a load is applied to the mount in a direction inclined or perpendicular to the facing direction of the first and second support metal members, the relative displacement of the first and second support metal members is prevented due to abutting contact of the oscillating plate with the inner wall of the pressure-receiving chamber, whereby the vibration-damping capability is considerably lowered. In the worst case, the abutting contact may lead to a damage of the oscillating plate and even the mounting device. To avoid the abutting contact of the oscillating plate, the size of the plate must be limited, thereby limiting a tuning range of frequencies of the vibrations against which the mounting device can exhibit a low dynamic spring constant.